It is well known in the art that complexes of nickel with phosphorous-containing ligands are useful as catalysts in hydrocyanation reactions. Such nickel complexes using monodentate phosphites are known to catalyze hydrocyanation of butadiene to produce a mixture of pentenenitriles. These catalysts are also useful in the subsequent hydrocyanation of pentenenitriles to produce adiponitrile, an important intermediate in the production of nylon. It is further known that bidentate phosphite, phosphinite and phosphonite ligands can be used to form nickel-based catalysts to perform such hydrocyanation reactions.
U.S. Pat. No. 3,773,809 describes a process for the recovery of Ni complexes of organic phosphites from a product fluid containing organic nitriles produced by hydrocyanating an ethylenically unsaturated organic mononitrile such as 3-pentenenitrile through extraction of the product fluid with a paraffin or cycloparaffin hydrocarbon solvent. Similarly, U.S. Pat. No. 6,936,171 to Jackson and McKinney discloses a process for recovering diphosphite-containing compounds from streams containing dinitriles.
U.S. Pat. No. 4,339,395 describes the formation of an interfacial rag layer during extended periods of continuous extraction of certain phosphite ligands. The '395 patent notes that the interfacial rag hinders, if not halts, the phase separation. Because the process is operated continuously, the rag must be removed continuously from the interface as it accumulates to avoid interrupting operation. To solve this problem for the disclosed components, the '395 patent discloses the addition of minor amounts of substantially water-free ammonia.
U.S. Pat. No. 7,935,229 describes a process for extractively removing heterogeneously dissolved catalyst from a reaction effluent of a hydrocycanation of unsaturated mononitriles to dinitriles with a hydrocarbon. The catalyst comprises a ligand which may be a monophosphite, a diphosphite, a monophosphonite or a diphosphonite. Ammonia or an amine may be added to a mixture of liquid phases before phase separation takes place.
A mixing section of a liquid-liquid extractor forms an intimate mixture of unseparated light and heavy phase. This intimate mixture comprises an emulsion phase. The emulsion phase may or may not comprise particulate solid material. This emulsion phase separates into a light phase and a heavy phase in a settling section. Accordingly, a settling section will contain at least some emulsion phase located between the upper light phase and the lower heavy phase. This emulsion phase tends to reduce in size over time. However, in some instances settling takes longer than desired or the emulsion phase never fully separates into a light phase and a heavy phase.
Addition of Lewis base, such as water, ammonia or amine, to the feed to a liquid-liquid extractor may result in enhanced settling of the emulsion phase. For example, this addition may result in the reduction of the size of the emulsion phase in the settling section, wherein the size of the emulsion phase is based upon the size of the emulsion phase in the absence of addition of Lewis base. Enhanced settling in the settling section may also be measured as art increased rate of settling, based upon the rate of settling in the absence of addition of Lewis base.
Another problem, which may be solved by addition of Lewis base, is formation of rag and build-up of a rag layer the settling section. Rag formation is discussed in U.S. Pat. No. 4,339,395 and U.S. Pat. No. 7,935,229. Rag comprises particulate solid material, and may be considered to be a form of an emulsion phase, which is particularly stable in the sense that it does not dissipate in a practical amount of time for conducting an extraction process. Rag may form in the mixing section or the settling section of an extraction stage. In the settling section, the rag forms a layer between the heavy phase and the light phase. The formation of a rag layer in the settling section inhibits proper settling of the heavy phase and the light phase. The formation of a rag layer may also inhibit the extraction of phosphorus-containing ligand from the heavy phase into the light phase. In a worst case scenario, rag can build up to the extent of completely filling a separation section, necessitating shut down of the extraction process to clean out the settling section. Addition of Lewis base to the mixing section may reduce or eliminate the size of a rag layer or reduce its rate of formation, based upon the size and rate of formation of the rag layer in the absence of addition of Lewis base.
Processes for the hydrogenation of compounds comprising nitrile groups to amine and aminonitrile compounds are known. Hydrogenation of dinitriles to the corresponding diamines is a process which has been used for a long time, in particular the hydrogenation of adiponitrile to hexamethylene diamine, a basic material in the preparation of nylon-6,6.
There has been an increasing interest in recent years in the hydrogenation (also sometimes known as semihydrogenation) of aliphatic dinitriles to aminonitriles, in particular the hydrogenation of adiponitrile to 6-aminocapronitrile, resulting either directly, or via caprolactam, in nylon-6.
U.S. Pat. No. 3,758,584 to Bivens et al. discloses a process for the catalytic hydrogenation of adiponitrile to hexamethylene diamine in the presence of a catalyst derived from a cobalt or iron compound, such as iron oxide, which has been activated in a mixture of hydrogen and ammonia at a temperature in the range of about 300° C. to about 600° C.
When a dinitrile is hydrogenated to form a diamine unwanted byproducts may be produced. For example, when adiponitrile is hydrogenated to form hexamethylene diamine, unwanted byproducts may include bis-hexamethylene triamine and diaminocyclohexane.